Insomnia is most often described as the inability to fall asleep easily, to stay asleep or to have quality sleep in an individual with adequate sleep opportunity. In the U.S., population-based estimates of either chronic or transient insomnia range from 10 to 40% of the population, or 30 to 120 million adults in the United States. Similar prevalence estimates have been reported in Europe and Asia. Across studies, there are two age peaks: 45-64 years of age and 85 years and older. Women are 1.3 to 2 times more likely to report trouble sleeping than men, as are those who are divorced or widowed, and have less education. In the U.S., the economic burden of insomnia approaches $100 billion, in direct health care costs, functional impairment, increased risk of mental health problems, lost productivity, worker absenteeism and excess health care utilization. It is recognized as a public health problem, contributing to more than twice the number of medical errors attributed to health care workers without insomnia episodes. Currently available treatments for insomnia, however, are not entirely satisfactory for a variety of reasons. Sedative-hypnotics are not a complete solution to the problem of insomnia as they are associated with significant adverse events such as the potential for addiction/dependence, memory loss, confusional arousals, sleep walking and problems with coordination that can lead to falls and hip fractures. The majority of insomnia patients would prefer a non-pharmaceutical approach to their insomnia complaints. Cognitive behavior therapy, while effective, is an expensive and labor intensive treatment that is not widely available and is not always covered by health insurance. Over-the-counter approaches to the treatment of insomnia including a variety of medications and devices suffer from inadequate clinical studies demonstrating significant effects in insomnia patients, as well as potentially dangerous side effects. A large need exists, therefore, for a safe, effective, non-invasive, non-pharmaceutical device for the treatment of insomnia.
Recent advances have been made in the neurobiology of sleep and in the neurobiology of insomnia that can inform innovative treatments for insomnia. Considerable evidence suggests that sleep may serve a restorative function. An EEG marker of sleep homeostasis is EEG spectral power in the delta frequency range (1-4 Hz). The homeostatic sleep drive may involve the restoration of brain energy metabolism through the replenishment of brain glycogen stores that are depleted during wakefulness. This function may have some regional specificity. A frontal dominance of EEG spectral power in the delta EEG spectral power range has been reported. A frontal predominance for the increase in delta power following sleep loss has also been reported. This region of cortex plays a prominent role in waking executive functions which are preferentially impaired following sleep deprivation. Evidence such as this, suggests that sleep is essential for optimal executive behavior and that the mechanism involves the frontal cortex.
“Hyperarousal”, on a variety of physiological levels, represents the current leading pathophysiological model of insomnia. Insomnia patients have been shown to have increased whole brain metabolism across waking and sleep in relation to healthy subjects; resting metabolic rate, heart rate and sympathovagal tone in HRV, cortisol secretion in the evening and early sleep hours, beta EEG activity during NREM sleep, increased levels of cortical glucose metabolism, especially in the frontal cortex, associated with higher levels of wakefulness after sleep onset, impairments in the normal drop in core body temperature around the sleep onset period; and cognitive hyperarousal resting on the pre-sleep thoughts of insomnia patients, often described as “racing,” unstoppable, and sleep-focused. Recent evidence also suggests that insomnia sufferers demonstrate selective attention directed toward sleep and bed-related stimuli, which may lead to a self-reinforcing feedback loop of conditioned arousal, poor sleep, and impaired waking function. Insomnia patients have demonstrated increases in beta EEG spectral power that correlate with increased metabolism in the ventromedial prefrontal cortex during NREM sleep. Improvements in sleep in insomnia patients have been associated with improvements in prefrontal cortex function as measured by functional neuroimaging.
A decline in metabolism in the prefrontal cortex, therefore, appears to be important for the normal function of sleep and hypermetabolism in this region may interfere with this normal function of sleep in insomnia patients. Interventions designed to reduce elevated metabolism in the prefrontal cortex may improve sleep in insomnia patients.
Several lines of evidence suggest that application of a cooling stimulus to the scalp may reduce metabolism in the cortex underlying the stimulus. Studies have shown that the application of a cooling stimulus to the scalp decreases brain temperature in the underlying cortex in both animals and humans. In a study in pigs, even a mild surface cooling of 15 degrees C. was associated with cooling of the scalp and superficial brain to 35 degrees C. In this study, there was a notable differential effect of surface cooling on superficial vs. deep brain tissue, with superficial brain tissue cooled to a greater degree than deep brain tissue. In a human study, Wang et al were able to decrease surface brain temperatures by an average of 1.84 degrees C. within 1 hour of subjects wearing a whole head cooling helmet. Biomedical engineering models demonstrate that cooling of the brain gray matter can be achieved by selective head cooling on the surface. These lines of evidence support the concept that application of a cooling stimulus at the scalp will be associated with reductions in metabolism in the underlying cortex.
Cerebral hypothermia is an intervention that has previously been used to treat other medical disorders due to its neuroprotective effects. Therapeutic hypothermia after global and focal ischemic and other neurotoxic events such as head trauma, stroke and neuronal insult during cardiopulmonary surgery has shown beneficial results in controlled animal and human studies. Preclinical studies have shown many neuroprotective effects of brain cooling. These include: metabolism, pH, neurotransmitter levels, free fatty acids, blood-brain barrier, edema, glucose metabolism, cerebral blood flow, free radical activation, lipid peroxidation, calcium accumulation, protein synthesis, protein kinase-C activity, leukocyte accumulation, platelet function, NMDA neurotoxicity, growth factors, cytoskeletal proteins, calcium-dependent protein phosphorylation, heat shock protein, immediate early genes, NOS activity, and MMP expression. It is conceivable that the neuroprotective benefits of cerebral hypothermia may aid patients with sleep disorders, including insomnia. Pathophysiologic models of the adverse events associated with sleep disorders are beginning to focus on the potential neuronal toxicity of having a sleep disorder. That this may occur in insomnia is suggested by findings of hypercortisolemia in insomnia patients in the evening and early hours of sleep and known adverse effects of hypercortisolemia on neuronal function. One preliminary study has demonstrated reduced volumes of the hippocampus in insomnia patients. This may be the result of neurotoxic factors.
Reducing hypermetabolism in the frontal cortex of insomnia patients during both the pre-sleep period and during sleep may reduce cognitive hyperarousal reported by insomnia patients. Cerebral localization of this is hypothesized to occur in the prefrontal cortex given its role in executive function and ruminative cognitions.
Application of a cooling stimulus to the frontal scalp area may also facilitate the normative changes in thermoregulation associated with sleep onset. Heat loss, via selective vasodilatation of distal skin regions (measured by the distal minus proximal skin temperature gradient (DPG), seems to be a crucial process for the circadian regulation of core body temperature (CBT) and sleepiness. Increased DPG before lights off has been noted to promote a rapid onset of sleep, suggesting a link between thermoregulatory and arousal (sleepiness) systems. As noted above, impairments in the normal drop in core body temperature around the sleep onset period has been demonstrated in insomnia patients. A device that produces heat loss, especially through the periphery, therefore, may improve sleep in insomnia patients.
Recent studies show that difficulty sleeping can be associated with increased brain metabolic activity especially in the frontal cortex. Patent application Ser. No. 11/788,694, filed Apr. 20, 2007, titled “Method and Apparatus of Noninvasive, Regional Brain Thermal Stimuli for the Treatment of Neurological Disorders,” now U.S. Pat. No. 8,236,038, which was previously incorporated by reference, described a method and apparatus of noninvasive, regional brain thermal stimuli for the treatment of neurological disorders. Functional neuroimaging studies have shown that a noninvasive device applying a hypothermic stimulus to the scalp overlying the frontal cortex of the brain (“frontal hypothermia”) reduced cerebral metabolic activity in insomnia patients during sleep, especially in the frontal cortex underlying the hypothermic pad. While these studies suggest that frontal hypothermia may be helpful in the clinical management of insomnia patients, the most appropriate parameters for the application of the device have not yet been fully worked out.
Preliminary data using frontal hypothermia suggests that it reduces relative metabolism in a region of cerebral cortex underlying the scalp where the device is applied. Application of the device would not necessarily be limited to the condition of insomnia, but could be applied to diverse neuropsychiatric disorders, each of which may have insomnia as a contributing component or which may be characterized by its own abnormal pattern of cerebral metabolism.
Several disorders have been shown to have insomnia as a co-morbid condition and/or relatively specific alterations in cerebral metabolism that may benefit from treatment with a frontal hypothermia device. These co-morbid conditions make medication treatment even more difficult, because these patients are often already on multiple other medications, some of which have sleep effects themselves. Co-morbid insomnia itself has been little studied with any form of treatment. Depression is associated with severe sleep disturbances including difficulty falling asleep, difficulty staying asleep, early morning awakening, or nonrestorative sleep. Functional neuroimaging studies have shown alterations in the normal reduction in prefrontal cortex metabolism from waking to NREM sleep. The lifetime prevalence of depression in the United States is 17.1% or currently 52 million individuals suggesting that this is a significant problem. The neurobiology of sleep problems in patients with chronic pain share significant overlaps with those of insomnia suggesting another medical disorder that may benefit from the frontal hypothermia device. The most common causes of pain that disrupt sleep include back pain (cost to society estimated to exceed $100 billion each year), headaches (50% of whom sleep disturbances trigger headaches and 71% of migraine sufferers have migraines that awaken them from sleep), fibromyalgia, and arthritis (osteoarthritis, rheumatoid arthritis and autoimmune diseases such as lupus). Chronic pain prevalence estimates in the United States are 10.1% for back pain, 7.1% for pain in the legs/feet, 4.1% for pain in the arms/hands, and 3.5% for headache. Chronic regional and widespread pain, are reported by 11.0% and 3.6% of respondents, respectively. Based on US Census data, this would translate into an additional market of over 50 million individuals. 70-91% of patients with post-traumatic stress disorder (PTSD) have difficulty falling or staying asleep. Medical treatments for the sleep problems in PTSD have revolved around medication management, which have associated adverse events. Studies conducted as part of the National Comorbidity Survey (NCS) have reported the prevalence of lifetime PTSD in the United States as 7.8 percent or currently a market of over 23 million individuals.
Aside from a primary, stand alone therapy for insomnia, this device may also benefit insomnia patients who are partial responders to traditional sedative-hypnotic therapy for insomnia or from cognitive-behavior therapy for insomnia. While clinical trial data suggest that approved hypnotics show statistically significant improvements in about ⅔rds of patients, significantly fewer patients report full remission of symptoms. This suggests that about ⅔rds of patients who are prescribed hypnotics would be non-responders or partial responders to these treatments and as such may benefit from adjunctive therapy with frontal hypothermia insomnia device, such as the devices and systems described herein.
Thus, there is a substantial need to provide methods, devices and systems for effectively creating frontal hypothermia to treat insomnia. The methods, devices and systems described herein may address many of the needs and issues described above.